January 31, 2013

Infrasound Study Reveals Why Some Homing Pigeons Get Lost

Homing pigeons have been bred to find their way back to a home loft, and despite their reliability, some of these domestic birds are thrown off course from to time.

In a new study, Jonathan Hagstrum, from the US Geological Survey (USGS), set out to find why pigeons released from a certain part of New York State always seem to have problems finding their way back home.

Hagstrum´s findings, which were recently published in the Journal of Experimental Biology (JEB), suggest that the bird´s use low frequency sound waves to navigate their routes, somewhat contradicting the theories that a majority of researchers have previously believed.

Back in the 1960s, Cornell University professor Bill Keeton was trying to identify the nature of the homing pigeons unique ability. Throughout the course of his experiments, Keeton released birds throughout New York State. He was surprised to find that whenever he released pigeons from Jersey Hill, they were disoriented and flew about directionless.

However, there was one exception: on August 13, 1969 the birds' navigational abilities mysteriously returned and they were able to fly back to their loft.

After learning that the pigeons can hear low frequency infrasound, or sound below 20 Hz, Hagstrum thought this ability could play a role in the bird´s navigational abilities. He posited that the bird´s use the Earth´s natural infrasound, generated by waves deep in the ocean, as a map. This theory runs counter to the prevailing belief–that the birds use their sense of smell or the Earth´s magnetic fields to guide them.

To test his theory, Hagstrum had to first model the atmospheric conditions on the exact days and locations that the pigeons had been released by Keeton during the 1960s. Using a state-of-the-art acoustics program — HARPA — Hagstrum and USGS computer scientist Larry Baker factored in the temperature, wind direction and speed measurements from historical local weather data.

The researchers then calculated how natural infrasound would have traveled from the pigeons´ home loft through the atmosphere, while refracting through the air and bouncing off the ground. They wanted to see if Jersey Hill was somehow shielded from the loft's infrasound signal and how the signal would have been perceived at Keeton´s two other release locations, Castor Hill and Weedsport.

Based on their models and calculations, the researchers were able to show that the loft's infrasonic signal was directed high into the atmosphere at Jersey Hill where the birds could not pick it up on the release days that the birds flew aimlessly. However, the study´s models show that on August 13, 1969, the conditions were perfect for the infrasonic signal to be picked up by the birds at the Jersey Hill site.

Hagstrum acknowledged to BBC News that his findings could be viewed as controversial.

"This doesn't prove it by any stretch - but it puts out a new idea, which, as far as I'm concerned, is the best explanation of what pigeons are doing, because it explains what has been going on at Jersey Hill,” he said.

Animal behavior expert and Oxford University professor Tim Guilford told the British news agency that there is a lot of evidence supporting the smell and magnetic field basis for the pigeons´ navigational abilities, but noted that Hagstrum used an “interesting approach.”

"Given the volume of evidence for other mechanisms, infrasound seems unlikely to be the whole explanation,” Guilford remarked.